1. Field of the Invention
The present invention relates to an organic electroluminescence multi-color display (also referred to as an organic EL multi-color display hereinafter) comprising a plurality of organic electroluminescent elements (hereinafter also referred to as organic EL elements) using an electroluminescent organic compound emitting light by injection of an electric current and provided with an emission layer made from such an organic electroluminescent material and moreover to a process for fabricating the organic EL multi-color display.
2. Description of the Related Art
The organic EL element using the organic compound material is typically a light emitting element having diode characteristic of an electric current injection type which emits light at the intensity corresponding to the amount of current. A display panel having a plurality of such EL elements arranged in a matrix has been developed. The display panel includes a substrate structure as shown in FIG. 1 which is fabricated in the following manner. An indium-tin-oxide (so-called ITO) film is deposited on a glass substrate 2 serving as a display screen, and the obtained ITO film is patterned by means of etching, thereby an anode 3 is formed on the substrate as a transparent electrode. Each organic EL device 1 constituting the display panel has a multi-layer structure wherein a plurality of organic compound material layers 4 including a light emitting layer and a cathode 5 (a metal electrode) have been deposited in this order on the anode 3 (a transparent electrode) by vacuum vapor deposition or the like. When required, the organic compound material layer 4 is provided with a hole transport function layer (a hole injection layer, a hole transport layer) and an electron-transport-function layer (an electron injection layer, an electron-transport layer) in addition to the light-emitting layer.
For example, Japanese Patent No. 2846571 discloses an organic EL element in which the thickness of the ITO anode and a plurality of organic compound material layers are so set that the desired wavelength of the light obtained from the light emitting layer can have a peak wavelength.
In the conventional organic EL element, the thicknesses of the ITO anode and a plurality of organic compound material layers are set in such a manner that the spectrum of the light obtained from the light emitting layer can have a desired peak wavelength. If such conventional organic EL element is adapted to an organic EL multi-color display, then a change of the thickness of the ITO anode is required so as to depend on the pixel for emitting light of a different color, that is, on each of the organic EL elements.
Since the ITO anode is deposited uniformly on the entire surface of a transparent substrate and thereafter formed into the desired thickness and pattern by etching, it is difficult to vary the thickness of the ITO anode partly for many elements on the same display substrate. In addition, this uneven ITO anode would make the manufacture of the display panel complicated since the ITO needs to repeat a deposition process partly in order to vary the thickness of the ITO anode in part.
An object of the present invention is to provide an organic EL multi-color display and a method for fabricating the organic EL multi-color display, which can be fabricated easily and provides an excellent external quantum efficiency of light.
An organic electroluminescence multi-color display according to the present invention comprises: a transparent substrate; and
a plurality of organic electroluminescence elements each including, a transparent electrode, a plurality of organic compound material layers including at least one light emitting layer and a metal electrode which are stacked in sequence on the transparent substrate,
wherein the organic electroluminescence elements comprising the light emitting layers made of different organic compound materials and taking on different colors of light emission, and
wherein some of functional layers, having the same function, of said organic compound material layers excluding the light emitting layer have different thicknesses corresponding to colors of emitted light respectively.
In an aspect of the organic electroluminescence multi-color display device according to the invention, each of said transparent electrodes in all of said organic electroluminescence elements has a constant thickness.
In another aspect of the organic electroluminescence multi-color display device according to the invention, said functional layers in all of said organic electroluminescence elements are made of the same organic compound material.
In a further aspect of the organic electroluminescence multi-color display device according to the invention, said functional layers in all of said organic electroluminescence elements have a continuous common layer made of the organic compound material with a constant thickness, and have complementary layers made of the same organic compound material as that of said common layer and stacked on said common layer in different thicknesses corresponding to colors of emitted light respectively.
In a still further aspect of the organic electroluminescence multi-color display device according to the invention, said functional layers in all of said organic electroluminescence elements have a continuous common layer made of the organic compound material with a constant thickness, and have complementary layers made of organic compound materials different from that of said common layer and stacked on said common layer in different thicknesses corresponding to colors of emitted light respectively.
In another aspect of the organic electroluminescence multi-color display device according to the invention, said functional layer is a hole transport layer stacked adjacent to the anode.
As to a further aspect of the organic electroluminescence multi-color display device according to the invention, the device further comprises a hole injection layer stacked in between said hole transport layer and said anode.
In a still further aspect of the organic electroluminescence multi-color display device according to the invention, said functional layer is an electron transport layer stacked adjacent to the cathode.
As to another aspect of the organic electroluminescence multi-color display device according to the invention, the device further comprises an electron injection layer stacked in between said electron transport layer and said cathode.
In a further aspect of the organic electroluminescence multi-color display device according to the invention, the light-emitting interface of the light-emitting layer emitting light having a wavelength of xcex serving as a primary component, and wherein the transparent electrode side portion in the organic compound material layers is deposited to have a film thickness such that an optical distance from the light-emitting interface to the interface with the largest difference in refractive indexes is substantially equal to even multiples of one-quarter of the wavelength xcex.
In a still further aspect of the organic electroluminescence multi-color display device according to the invention, the metal electrode side portion in the organic compound material layers is deposited to have a film thickness such that an optical distance from the light-emitting interface to an interface bordering on the metal electrode is substantially equal to odd multiples of one quarter of the wavelength xcex.
In addition, a method for fabricating an organic electroluminescence multi-color display, according to the present invention, includes: a transparent substrate; and a plurality of organic electroluminescence elements each including, a transparent electrode, a plurality of organic compound material layers including at least one light emitting layer and a metal electrode which are stacked in sequence on the transparent substrate, in which the organic electroluminescence elements containing the light emitting layers made of different organic compound materials and taking on different colors of light emission,
said method comprising the steps of:
stacking a continuous common layer made of the organic compound material in all organic electroluminescence elements and having a constant thickness, and
stacking at least one complementary layer in contact with said common layer at a different thickness corresponding to colors of emitted light, before or after the step of stacking the common layer, whereby some of functional layers, having the same function, of said organic compound material layers excluding the light emitting layer have different thicknesses corresponding to colors of emitted light respectively.
In an aspect of the method according to the invention, said transparent electrode is deposited in all of said organic electroluminescence elements to have a constant thickness.
In another aspect of the method according to the invention, said complementary layer is formed from the same organic compound material as that of said common layer.
In a further aspect of the method according to the invention, said complementary layer is formed from an organic compound material different from that of said common layer.
In a still further aspect of the method according to the invention, said organic compound material layer is stacked on the anode as a hole transport layer.
In another aspect of the method according to the invention, a hole injection layer is stacked in between said hole transport layer and said anode.
In a further aspect of the method according to the invention, said organic compound material layer is stacked on the cathode as an electron transport layer.
In a still further aspect of the method according to the invention, an electron injection layer is stacked in between said electron transport layer and said cathode.
In another aspect of the method according to the invention, the light-emitting interface of the light-emitting layer emitting light having a wavelength of xcex serving as a primary component, and wherein the transparent electrode side portion in the organic compound material layers is deposited to have a film thickness such that an optical distance from the light-emitting interface to the interface with the largest difference in refractive indexes is substantially equal to even multiples of one-quarter of the wavelength xcex.
In a further aspect of the method according to the invention, the metal electrode side portion in the organic compound material layers is deposited to have a film thickness such that an optical distance from the light-emitting interface to an interface bordering on the metal electrode is substantially equal to odd multiples of one quarter of the wavelength xcex.
In a still further aspect of the method according to the invention, said organic compound material layer and said metal electrode are stacked by vapor deposition using a mask.
According to the present invention, the organic compound material layers are formed in two or more processes for depositing such as the common layer and the complementary layer to adjust the thickness of the complementary layer of the organic compound material layers. Such organic EL elements can thereby be obtained that can provide improved light emission efficiency.